Biochemical and morphometric analyses in hypoplastic lungs

Decreased lung fibroblast growth factor 18 and elastin in human congenital diaphragmatic hernia and animal models

RATIONALE

Lung hypoplasia in congenital diaphragmatic hernia (CDH) seems to involve impaired alveolar septation. We hypothesized that disturbed deposition of elastin and expression of fibroblast growth factor 18 (FGF18), an elastogenesis stimulus, occurs in CDH.

OBJECTIVES

To document FGF18 and elastin in human CDH and ovine surgical and rat nitrofen models and to use models to evaluate the benefit of treatments.

METHODS

Human CDH and control lungs were collected post mortem. Diaphragmatic hernia was created in sheep at 85 days; fetal lungs were collected at 139 days (term = 145 days). Pregnant rats received nitrofen at 12 days; fetal lungs were collected at 21 days (term = 22 days). Some of the sheep fetuses with hernia underwent tracheal occlusion (TO); some of the nitrofen-treated pregnant rats received vitamin A. Both treatments are known to promote lung growth.

MEASUREMENTS AND MAIN RESULTS

Coincidental with the onset of secondary septation, FGF18 protein increased threefold in control human lungs, which failed to occur in CDH. FGF18 labeling was found in interstitial cells of septa. Elastin staining demonstrated poor septation and markedly decreased elastin density in CDH lungs. Consistently, lung FGF18 transcripts were diminished 60 and 83% by CDH in sheep and rats, respectively, and elastin density and expression were diminished. TO and vitamin A restored FGF18 and elastin expression in sheep and rats, respectively. TO restored elastin density.

CONCLUSIONS

Impaired septation in CDH is associated with decreased FGF18 expression and elastic fiber deposition. Simultaneous correction of FGF18 and elastin defects by TO and vitamin A suggests that defective elastogenesis may result, at least partly, from FGF18 deficiency.

MRI of normal and pathological fetal lung development

Normal fetal lung development is a complex process influenced by mechanical and many biochemical factors. In addition to ultrasound, fetal magnetic resonance imaging (MRI) constitutes a new method to investigate this process in vivo during the second and third trimester. The techniques of MRI volumetry, assessment of signal intensities, and MRI spectroscopy of the fetal lung have been used to analyze this process and have already been applied clinically to identify abnormal fetal lung growth. Particularly in conditions such as oligohydramnios and congenital diaphragmatic hernia (CDH), pulmonary hypoplasia may be the cause of neonatal death. A precise diagnosis and quantification of compromised fetal lung development may improve post- and perinatal management. The main events in fetal lung development are reviewed and MR volumetric data from 106 normal fetuses, as well as different examples of pathological lung growth, are provided.

Fetale Lungenentwicklung in der MRT

A well-organized interplay between many molecular factors as well as mechanical forces influence fetal lung development. At the end of this complex process a sufficiently sized and structurally mature organ should ensure the postnatal survival of the newborn. Besides prenatal ultrasonography, magnetic resonance imaging (MRI) can now be used to investigate normal and pathological human lung growth in utero. Oligohydramnios, due to premature rupture of membranes (PROM), is an important risk factor for compromised fetal lung growth. In these situations MR volumetry can be used to measure the size of the fetal lung quite accurately. Together with the evaluation of lung signal intensities on T2-weighted sequences, fetuses with pulmonary hypoplasia can be readily detected.

Expression of angiogenesis-related factors in lungs of patients with congenital diaphragmatic hernia and pulmonary hypoplasia of other causes

Congenital diaphragmatic hernia (CDH) is a congenital disorder, complicated by pulmonary hypoplasia (PH) and pulmonary hypertension. Hypoplastic lungs have fewer and smaller airspaces than normal, with thicker interalveolar septa; the adventitia and media of pulmonary arteries are thickened, and the total size of the pulmonary vascular bed is decreased compared to normal. Although histological abnormalities in PH have been described, less is known about the underlying molecular mechanisms. Therefore, we have investigated a series of proteins, known to be involved in angiogenesis, including von Hippel-Lindau protein (pVHL), hypoxia-inducible factor-1a (HIF-1a), vascular endothelial growth factor (VEGF), fetal liver kinase 1 (Flk-1), and endothelial and inducible nitric oxide synthase (eNOS, iNOS) by immunohistochemistry on paraffin-embedded lung tissue of CDH patients ( n = 13), patients with lung hypoplasia due to other causes ( n = 20), and normal controls ( n = 33). pVHL was expressed more frequently in the arterial smooth muscle cells of CDH lungs compared with both other groups. Furthermore, HIF-1a was expressed less frequently in the endothelium of arteries, veins, and capillaries of CDH lungs as compared with both other groups. No differences were observed in the expression patterns of VEGF, Flk-1, eNOS, and iNOS between the different groups. Our data suggest a role for pVHL and HIF-1a in normal and abnormal pulmonary angiogenesis. The differential expression of these proteins may provide a molecular basis for the histological differences observed in the lung vessels of patients with CDH.

CFTR modulates lung secretory cell proliferation and differentiation

We have permanently reversed the lethal phenotype in the cystic fibrosis (CF) transmembrane conductance regulator (CFTR)-deficient (knockout) mouse after in utero gene therapy with an adenovirus containing the cftr gene. The gene transfer targeted somatic stem cells in the developing lung and intestine, and these epithelial surfaces demonstrated permanent developmental changes after treatment. The survival statistics from the progeny of heterozygote-heterozygote matings after in utero cftr gene treatment demonstrated an increased mortality in the homozygous normal pups, indicating that overexpression during development was detrimental. The lungs of these pups revealed accelerated secretory cell proliferation and differentiation. The extent of proliferation and differentiation in the secretory cells of the lung parenchyma after in utero transfer of the cftr gene was evaluated with morphometric and biochemical analyses. These studies provide further support of the regulatory role of the cftr gene in the development of the secretory epithelium.

Distribution and number of Clara cells in the normal and disturbed development of the human fetal lung

In this study the numerical growth and topological distribution of Clara cells were investigated in normal and hypoplastic lungs of fetuses ranging in age from the 10th to the 24th gestational week. In addition, the lungs of premature infants suffering from hyaline membrane syndrome (HMS) and bronchopulmonary dysplasia (BPD) were used as a model of disturbed lung growth in the early postnatal phase. Clara cells were observed to appear in the airway epithelium of fetuses of the 15th gestational week. After the 15th week of gestation the Clara cell number increased monotonously with increasing gestational age, reaching 5.4% Clara cells in the bronchial epithelium and 11.2% in the bronchiolar epithelium at the 24th gestational week. In the investigated period of gestation the Clara cell number was significantly higher in the bronchiolar epithelium compared to the bronchial epithelium. Hypoplastic lungs showed no difference in number and distribution of Clara cells compared to normal age-matched controls. This finding suggests the growth of Clara cells to be relatively accelerated compared to the decreased maturation of the lung parenchyma. The HMS/BPD cases showed normal Clara cell counts in the bronchial epithelium, whereas in the bronchiolar epithelium this value was decreased. This finding is caused by the extreme turnover of the airway epithelium in HMS/BPD; the local distribution of the epithelial damage is speculated to be caused by the physicochemical properties of inhaled oxygen.

Epithelial cell morphology and airspace size in hypoplastic human fetal lungs associated with oligohydramnios

The relative frequency of different types of respiratory epithelial cells in normal fetal lungs (control, CON) and hypoplastic lungs associated with oligohydramnios (OH) was determined at the electron microscopic level and airspace size was measured. At 24+ weeks CON lungs had 82.4 +/- 1.2% undifferentiated cells, 15.9 +/- 1.2% type II cells, and 1.7 +/- 0.4% type I cells (n = 3), whereas OH lungs had 94.6 +/- 2.1% undifferentiated cells, 5.4 +/- 2.1% type II cells, and no type I cells (n = 3). At 36+ weeks CON lungs had 7.8 +/- 3.4% undifferentiated cells, 46.1 +/- 3.1% type II cells, and 46.1 +/- 1.4% type I cells (n = 3), whereas OH lungs had 37.7 +/- 1.2% undifferentiated cells, 42.5 +/- 1.7% type II cells, and 19.8 +/- 0.8% type I cells (n = 3). Differences between CON and OH lungs in the proportions of undifferentiated and type I cells at 36+ weeks were highly significant (p less than .001), whereas type II cell proportions did not differ significantly in either age group. The proportion of lung occupied by airspaces increased from 38.3% at 24+ weeks to 68.7% at 36+ weeks in CON lungs but only from 26.7% to 35.7% in OH lungs. The differences between the groups were significant at both 24+ weeks (p less than .01) and 36+ weeks (p less than .001). Mean airspace size in CON lungs varied from 2.8 x 10(-6) mm2 at 24+ weeks to 4.4 x 10(-6) mm2 at 36+ weeks and in OH lungs from 1.7 x 10(-6) mm2 at 24+ weeks to 2.7 x 10(-6) mm2 at 36+ weeks. These results give quantitative expression to the severity of impaired morphologic maturation in OH lungs.